The effect of landscape topography and in-stream habitat on the distribution, growth, and survival of Lahontan cutthroat trout (Oncorhynchus clarki henshawi) in a high desert watershed

Abstract:

Lahontan cutthroat trout (LCT) (Oncorhynchus clarki henshawi) are currently limited in their distribution to a patchwork of small isolated populations, the result of habitat degradation and natural variation in landscape and in-stream conditions. The objectives of this study were to determine how landscape level topographic features influence LCT distribution patterns. The work was carried out in a sub-basin of the Quinn River system, McDermitt Creek, which drains the sagebrush desert of southeastern Oregon and northern Nevada. Headwater tributaries of this creek consist of alternating canyon-confined and valley bounded reaches and LCT within these systems are challenged by low discharge and high temperatures during the summer, and anchor ice during the winter. Contiguous whole stream surveys were used to look at trout distribution during the summer of 2003 and spring and fall of 2004. Our results showed that topography affected LCT distribution in all reaches. LCT numbers were highest in areas with greater numbers of nick-points (the transition zones between less confined and more confined valley segments) and greater valley confinement. Additionally, in the downstream portion of our headwater reaches, more LCT were found in nick-points than expected based on the availability of this habitat type. Our data suggest that hyporheic inputs may be high in such areas, thus providing LCT with shelter from warm water in the summer, anchor ice in the winter and shallow stream depths during all seasons. Spatial occurrence of these areas of refugia can be taken into consideration when planning land-use activities and restoration efforts.
After almost 30 years of conservation effort, Lahontan cutthroat trout (LCT) (Oncorhynchus clarki henshawi) populations remain in peril throughout the Great Basin region of southeastern Oregon and northern Nevada. This is not surprising since very little research has been done on the ecology of LCT, and management has been carried out without essential information on this sub-species. The objectives of our study were to determine whether there are inter-stream or inter-reach differences in LCT habitat selection, and if those differences corresponded to differences in fish survival and growth. We relied upon contiguous whole stream surveys to look at fish distribution and in-stream habitat. The use of half duplex PIT tags allowed us to determine the growth, movement patterns, and survival rates of most adult (>100 mm) LCT within the system. We found greater trout growth (median daily change in biomass 0.46% vs. 0.07%), but lower survival (35% vs. 61% between July and November), in relatively warmer and more open reaches than in cooler reaches. Additionally, undercut banks (predation shelter) were more important to trout in cooler stream reaches than in warmer ones, where habitat choice responded first to cold water input (which was influenced by topography). Our results will be useful in identifying and describing areas of high quality LCT habitat in low order streams throughout the Great Basin, thus allowing informed management decisions to facilitate the recovery of the sub-species.